This invention relates generally to pipe joint seals for coupling adjacent ends of aligned pipe sections, and more particularly to seals of the type employing a compressible packing ring which is adapted to undergo radial expansion into sealing engagement with adjacent wall portions of the pipe sections.
In the past, a number of sealing pipe constructions have been proposed and produced. U.S. Pat. No. 3,781,040 shows a pipe joint including a resilient annular sealing ring having a flange portion which is adapted to be compressed between one end of a thin-walled pipe and an internal shoulder in the bore of a companion pipe fitting. Compression of the ring is effected by tightening a series of circumferentially spaced screws which are disposed at an angle with respect to a radial section through either of the pipes. While the above arrangement was found to be satisfactory in many respects, problems were sometimes encountered in that it was not always evident as to how much the screws should be tightened. Moreover, there was the possibility that unequal pull-up of the screws would cause the thin-walled pipe to shift to an eccentric position with respect to the companion fitting, possibly giving rise to leaks. In addition, the dimensions of the groove in which the screws were received had to be kept to close tolerances, as did the dimensions of the annular sealing gasket, in order to insure a tight seal.
Another construction is shown in U.S. Pat. No. 3,847,392, illustrating an extensible pipe fitting for a sprinkler system, wherein a resilient sealing gasket is expanded radially into tight frictional and sealing engagement with adjacent wall portions of telescoping inner and outer pipes. Expansion of the gasket was effected by a locking nut. In such a construction, it was not evident as to how much the nut should be tightened. Moreover, there was also the danger that excessive tightening of the nut would cause permanent deformation or crumbling of the gasket, thus defeating its effectiveness as a seal. Accordingly, the installer had to be extremely careful not to overtighten such nuts, while still insuring that a leak resistant seal was established.
Still other arrangements involved special pipes or tubing which had washer-like shoulders which were welded in place, and against which the sealing ring would bear. Special tubing involving welding operations was expensive to produce, and added unnecessary extra costs to the manufacturing process.